Research On Stability Of Silt Solidified By Vacuum Preloading With Ionic Soil Stabilizer

With the deepening of environmental remediation,many cities have begun to pay attention to the disposal of lakes and river sludge.Silt has the characteristics of high water content,high clay content,low strength and low permeability.In order to reduce the secondary pollution of dredging to the environment,silt is usually harmlessly treated and resource utilized.Sludge solidification treatment technology is a widely used large-scale sludge treatment method in ChinaVacuum preloading and Ionic Soil Stabilizer(ISS)are effective ways to solidify silt.Based on the application of vacuum preloading assisted grouting technology and equipment,the silt was solidified through the action of ISS and vacuum preloading.After experiments,the strength and stability of silt after solidification are analyzed.The main content and research results obtained are as follows:(1)Experimental study on compressive strength of ISS solidified silt.The unconfined compressive strength test of solidified silt samples with different ISS content after 7 days of curing time is carried out,and the relationship between compressive strength and content of ISS solidified siltis analyzed and compared with cement.The research shows that the unconfined compressive strength of solidified silt is greatly improved and the porosity is reduced under the action of appropriate proportion of ISS.(2)Experimental study on vacuum preloading of silt.Based on the direct vacuum preloading method,the vacuum drainage channel and surface sealing method are designed.The indoor vacuum preloading test device is designed,and the ISS combined vacuum preloading solidification test scheme is formed.The test device has the advantages of small vacuum transmission loss and fast drainage rate.The designed device is used to carry out the vacuum preloading test on the silt,and the changes of surface settlement,vacuum transmission and drainage were analyzed.The test shows that under the vacuum negative pressure,the shallow silt with high initial moisture content has a significant decrease in soil moisture content and a significant increase in compactness.When the soil settlement occurs,the silt is consolidated as a whole.(3)Experimental study on ISS combined with vacuum preloading solidification of silt.Vacuum preloading device combined with grouting equipment is used to carry outmodel test.Under the combined action of vacuum pressure and grouting pressure,ISS is quickly injected into the silt and consolidated.Then the diffusion range and solidification effect of ISS are analyzed from the surface settlement,drainage and physical and mechanical indexes of solidified silt.The results showed that the combined treatment method can improve the consolidation effect of silt,the surface settlement of silt increases and the drainage rate increases significantly.Compared with the vacuum preloading method,the positive pressure and ISS effectively improves the consolidation efficiency,and makes the solidified sludge have a larger compressive strength.(4)Compressive strength test of ISS solidified silt under dry-wet cycles.The appearance change and mass loss of solidified sludge samples with different contents under different dry-wet cycles were analyzed.The unconfined compressive strength test of cement and ISS solidified silt samples was carried out after dry-wet cycles to analyze the resistance of solidified silt to dry-wet cycles.The results showed that ISS can improve the resistance of solidified silt to dry-wet cycles,and the improvement effect of ISS is better than that of cement.The unconfined compressive strength of the ISS solidified sludge sample after 28 days curing time can still reach 1.214 MPa after 10 times dry-wet cycle.(5)Compressive strength test of ISS solidified silt under soaking conditions.The unconfined compressive strength test of cement and ISS solidified silt after immersion was carried out.The solidified silt sample after immersion was analyzed from the appearance change,mass loss and strength change.The results showed that ISS helps to maintain the stability of solidified silt in water,which stabilizing morphology and structure.The stability of the original soil was poor.The original soil collapsed within 12 h of immersion.The ISS solidified sludge maintained good morphology and smooth surface within 7 days of immersion.The maximum unconfined compressive strength is 0.321 MPa at 7 days of immersion.Compared with cement solidified silt,the compressive strength of ISS solidified silt is higher.The ISS solidified silt has low mass loss,low water absorption,smooth surface and is not easy to crack.(6)Leaching characteristics of heavy metals in ISS solidified silt under soaking conditions.The solidified silt has soaked in ultrapure water for 7 days.To analyze the stabilization effect of ISS on the solidification of heavy metals in the silt,the concentration changes of Cu,Pb,Cd in water are measured.The test shows that ISS played a stable role in the leaching of harmful heavy metals Cu,Pb and Cd in the silt,and the curing efficiency of ISS is Pb < Cu < Cd.The more ISS content,the better solidification effect of heavy metals in silt.Compared with cement,ISS has higher curing efficiency for Cu and Pb.